Fluid handling system and method

ABSTRACT

A fluid handling method and system in which fluid flow through a hollow casing is distributed in accordance with a predetermined profile along an elongate slot in the casing of relatively high aspect ratio by the provision of internal flow diverting baffle means interposed between communicating conduit means of relatively low aspect ratio and the slot and blocking direct fluid flow therebetween while diverting the flow into a predetermined profile along the slot.

United States Patent Inventor Clifiord Culpepper, Jr.

Charlotte, N.C.

Appl. No. 820,377

Filed Apr. 30, 1969 Patented June 22, 1971 Assignee Aero-Dyne Manufacturing, Inc.

Charlotte, N.C.

FLUID HANDLING SYSTEM AND METHOD SCIdlBJDnwhgFip.

us.c1 911/33, 98/35, 98/62, 98/1 15, 98/8 in. c1 F24: 13/00 worm 98/33,:45, 62,8,10, 115 K [56] References Cited UNITED STATES PATENTS 2,184,484 12 1939 Bojner 98/33 2,874,627 2/1959 Simmonds 98/115 Primary Examiner-William .l. Wye Atromeyl arrott, Bell, Seltzer, Park and Gibson ABSTRACT: A fluid handling method and system in which fluid flow through a hollow casing is distributed in accordance with a predetermined profile along an elongate slot in the easing of relatively high aspect ratio by the provision of internal flow diverting baffle means interposed between communicating conduit means of relatively low aspect ratio and the slot and blocking direct fluid flow therebetween while diverting the flow into a predetermined profile along the slot.

PATENIED JUN22-I9Yl SHEET 1 [1F 2 CuFFosab QULPEPPE R IQ,

BY wfif iq g 114 ATTORNEYS PATENTED JUN22 I971 SHEET 2 0F 2 INVENTOR. Cu FFOEI) CLJLPEPPE 2,332.

ATTORNEYS FLUID HANDLING SYSTEM AND METHOD The present invention relates to a fluid handling system and method in which fluid flow is distributed in a predetermined manner along an elongate slot.

Designers of fluid handling systems, and particularly gas (air) handling systems, have long recognized that, within the limitations established by the physical properties of the fluid being handled, controlled distribution of flow from a region of higher pressure through an opening to a region of lower pressure is obtained only by careful establishment of flow conditions relative to that opening. Elongate slots of high aspect ratio are commonly used to provide a relatively large flow area which is adapted to be fitted into conventional construction and, in the specific instance of flow to be uniformly distributed along elongate, high aspect ratio, slots or port openings, reliance has heretofore been placed upon establishing conditions approximating those known as plenum conditions."

Heretofore, plenum conditions have been obtainable only by providing large plenum volumes both upstream and downstream of the slot so that the total pressure of the fluid is given the opportunity to uniformly distribute itself along the slot on both the upstream and downstream sides thereof. As herein used, total pressure includes both static pressure and velocity pressure and is defined as the total kinetic and potential energy of a unit volume of the fluid, existing by virtue of the fluid density, velocity, and degree of compression if applicable.

As has been appreciated by fluid system designers, the attainment of plenum conditions for an elongate slot presents substantial difficulty, particularly in connection with gases, in that the plenum volumes required become excessively large as the length of the slot becomes greater.

In attempting to apply the methods of conventional design to fluid handling systems in which fluid flow is to be induced through an elongate slot, no entirely satisfactory solution has been found heretofore for reducing the plenum volumes required. Thus, minimization of the plenum volumes has required acceptance of variations in flow conditions along an elongate slot, particularly where the aspect ratios of the elongate slot and a connecting conduit communicating with a plenum chamber for flow of fluid relative thereto and through the slot are different.

As herein used, the term aspect ratio" refers to a number obtained by dividing the greater dimension of a port or fluid flow opening by the least dimension thereof. Thus, the aspect ratio of a round conduit or square conduit is expressed as one, while all other aspect ratios are expressed as numbers greater than unity. Such expression implies that the ratio is 1:1, with the first expressed dimension varying to show the extent to which the greater dimension exceeds the lesser dimension of a flow opening or port. The influence of aspect ratio on nonuniform distribution of flow through an elongate slot results from the vena contracts effect of flow moving relative to the communicating conduit of lesser aspect ratio, and thus precluding uniform distribution of flow along the elongate slot. It is this factor which makes the special case of uniformly distributed flow more difficult to obtain than other profiles of flow and has led to study of that special case.

The profiling of fluid flow along an elongate slot resulting from differences in aspect ratio between the elongate slot and a communicating conduit and the relative positioning of the conduit to the elongate slot is highly desirable to obtain a desired predetermined profile of flow. Where such aspect ratio differences and positioning are consciously chosen, some degree of controlled nonuniform distribution of fluid flow along an elongate port is achievable. However, such techniques still fail to meet the conditions required in a substantial number of instances.

With the above discussion in mind, it is an object of the present invention to minimize the space required by a plenum volume in one flow direction from an elongate slot while providing a fluid handling system in which the profile of flow along the elongate slot is controllable in predetennined manner. In realizing this object of the present invention, the

possibility is opened of economically constructing a fluid handling system heretofore considered desirable but unobtainable for economical reasons.

Yet another object of the present invention is to obtain a uniformly distributed volume of fluid flow, particularly air, through an elongate slot of vary high aspect ratio, in order to promote more uniform circulation of the air through a selected area or an enclosed area such as a building. In realizing this object of the present invention, the volume required in a plenum chamber on one side of the elongate slot is minimized by the adoption of a method of operation in which fluid flow is diverted from the shortest flow path otherwise possible between the elongate slot and a coupling conduit operatively communicating with the plenum chamber and is distributed along the slot in a predetermined manner through the use of a baffle of unique design for given conditions of aspect ratios, relative positions, desired profile, etc.

Some of the objects and advantages of the invention having been stated, others will appear as the description proceeds, when taken in connection with the accompanying drawings, in which:

FIG. 1 is an elevation view, in section, through a building structure incorporating a fluid handling system in accordance with the present invention;

FIG. 2 is an enlarged perspective view of portions of the fluid handling system incorporated in the building structure of FIG. 1;

FIG. 3 is an enlarged elevation view, in section, through a hood structure portion of the fluid handling system of FIGS. 1 and 2;

FIG. 4 is an enlarged elevation view, in section as indicated by a dashed line enclosure, through a portion of the hood structure of FIG. 3;

FIG. 5 is a plan view, in section along a line 5-5, through a portion of the hood structure of FIGS. 3 and 4;

FIG. 6 is an elevation view, in partial section along a line 6-6, through a portion of an air distribution box incorporated in the fluid handling system of FIGS. 1 and 2; and

FIG. 7 is a perspective view, partially in phantom, of the air distribution box of FIGS. 2 and 6 showing the flow of air therewithin.

Referring now more particularly to the drawings, the present invention is there illustrated in connection with a fluid handling system for the circulation of air within a building structure. In particular, a convenience food store or carryout building structure such as is illustrated in FIG. 1 provides a particularly favorable environment for the following disclosure of the present invention. While the discussion hereinafter will proceed with particular reference to the movement of air through such a closed building space, it is to be understood from the outset that the means herein disclosed for controlling the distribution of fluid flow along the length of an elongate slot is contemplated as having utility with gases other than air and with fluids other than gases. Further, while the application of the present invention to handling of air in conjunction with the operation of a carryout food service business is particularly directed to conveying air suspended materials, as pointed out hereinafter, it is contemplated that the present invention has utility both with regard to conveying of air suspended materials and with regard to the mere distribution of fluid flow where applicable for other purposes. As illustrated in FIG. 1, the structure incorporating the present invention includes exterior walls 10 and I1 enclosing a space, a structural roof l2, and an appearance ceiling l4 suspended below the structural roof 12. In the particular structure illustrated, a cooking grill 15 is located adjacent the rear exterior wall 10, and a sandwich preparation and delivery table 16 is located intermediate the depth of the building. Customers enter through doors in the front exterior wall 11, approach the delivery table 16 and order food products prepared by grilling on the grill 15.

In order to provide a flow of air through the space enclosed within-the building structure, for removing therefrom smoke, airborne grease particles, fumes or the like resulting from the operation of the grill 15, the present invention includes an air handling system as illustrated in F 16$. 2 through 7 arranged relative to the building structure of FIG. 1. In particular, the air handling system includes an air supply means generally indicated at 20 and including an air distribution box 21 located adjacent the front exterior wall 11 for supplying air into the interior of the building and an air exhaust means generally indicated at 30 and including a hood 31 positioned over the grill 15 for removing smoke, airborne grease particles and the like from the interior of the building. As indicated generally by arrows in FIGS. 1 and 2, flow of air within the enclosed space is from the air distribution box 21 forwardly against the interior side of the front exterior wall 11, then turning to cross the food preparation and delivery counter 16, pass above the grill 15 and into the hood 31.

In the form illustrated, both the air supply means and the air exhaust means 30 include fluid flow inducing means in the form of a fan, respectively identified as a supply fan 22 and an exhaust fan 32. In both instances, operative communication is established between the respective fans 22, 32 and a hollow casing defined respectively by the air distribution box 21 and the hood 31 and in each instance having an elongate sidewall. 1n the instance of the air supply means 20, the air distribution box 21 is preferably of generally square cross-sectional configuration, and has a length appropriate to extend across at least a substantial portion of the width of the store building in which the air handling system is installed. The box 21 includes an elongate sidewall 24, arranged facing the interior surface of the front building wall 11, which has an elongate slot 25 opening therethrough. In the instance of the air exhaust means 30, the hood 31 includes an elongate sidewall 3 facing rearwardly within the hood 3], with an elongate slot 35 fonned between the lower edge of the sidewall and a turned under portion 36 of the forward facing wall of the hood. While it is contemplated that the grill 15 will extend substantially across the entire width of the rear wall 111 in many installations of the air handling system of the present invention, it is acknowledged that the longitudinal extent of the hood 31 need only be substantially the same as the width of the cooking area over which the hood 31 is arranged.

Operative communication between the respective fans 22 and 32 and the corresponding elongate hollow casings 21 and 31 is established by coupling conduits 27, 28 and 38, respectively, directly connected to and directly communicating with the elongate hollow casings. 1n the instance of the air supply means 211, two communicating conduits 27, 23 are provided, and preferably take the form of spaced-apart round conduits each connected to a junction box to which air is delivered from the fan 22. In the particular installation shown, this arrangement has been chosen in order to conserve space and facilitate ease of installation, and it is to be understood that the configuration and arrangement of the communicating conduits 27, 28 may vary. Similarly, the coupling conduit 38 of the air exhaust means 30 is illustrated as a generally rectangular duct, located centrally of the length of the hood 31. It is to be understood that the present invention contemplates that the coupling conduit for the hood 31 may be connected thereto at a difl'erent point along its length and may be subdivided into a number of coupling conduits if desired to accommodate particular space requirements.

As installed in a convenience food store for the flow of air over the grill 15, the air exhaust means 30 functions as a system for conveying material by gaseous flow, in that the system is particularly designed to convey grease particles suspended in the air flow to and through the fan 32, to be delivered to a grease collection or disposal means which forms no pertinent part of the present invention. To accomplish the conveying function, the elements of the exhaust means 311, including the fan, coupling conduit 38, hood 31 and elongate slot 35 cooperate one with another to maintain the velocity of fluid flow through all portions of the exhaust system 311 from the slot 35 onward to the grease collection or disposal means at least above that velocity at which grease particles are maintained in suspension and move with the flowing air. While particularly disclosed herein with reference to an exhaust system, wherein a negative pressure is induced within the hood 31, it is to be understood that the present invention contemplates the maintenance of flow velocities at material conveying levels to be equally applicable to other fluid flow delivering systems, similar in some respects to the air supply means 20, for the conveyance of materials to an elonggte slot outlet and the delivery of such materials through the elongate slot outlet.

In both the air supply means 20 and exhaust means 30 of the present invention, the volume of air flowing through the elongate slots 25, 35 is distributed in accordance with a predetermined profile along the length of the slots. ln the particular environment shown, it is preferred that the distribution of air volume flow be uniform along the entire length of the elongate slots, in an effort to obtain uniform velocity of flow throughout the entire enclosed space within the store. It is contemplated, however, that the distribution of volume of fluid flow through an elongate slot may be nonuniform therealong, if so desired, while relying upon the structure now to be described to obtain such distribution.

ln order to accomplish the distribution of flow through an elongate slot in accordance with the predetermined profile, the present invention incorporates baffle means within the hollow casings 21, 31 for directing the flow of fluid within the hollow casings along predetermined paths. In particular, the baffle means within the hollow casings cooperate with the casings in defining predetermined open areas arranged to block fluid flow along the most direct flow path otherwise existing between the elongate slot and the communicating conduit means directly coupled to the casing, and to divert the volume of fluid flow to certain other flow paths within the casing. This mechanical forcing of the distribution of air is accomplished, as discussed more fully below, generally by shaping the open areas in generally triangular form. As trapezoidal openings are frequently taken for purposes of flow analysis as essentially triangular, and permit avoiding entanglement problems in the conveying of fibrous materials, it is also contemplated that the open areas may be formed as trapezoidal areas in fact and the phrase generally triangular" as used herein is intended to encompass a truly trapezoidal area.

More particularly, the hollow casings of the distribution box 21 and hood 31 have predetermined cross-sectional areas, viewed relative to the fluid flow therethrough. Baffle means disposed in the casing have a cross-sectional area less than that of the casings, so that predetermined open areas defined by the baffle means and easing operate as tuned ports, as contrasted with the substantially constant width along the slots 25, 35. While any definition of the distribution of the open area for the tuned ports would necessarily be very specific and relate only to a particular design configuration, a general discussion of the manner in which the distribution of open area in the tuned ports may be detennined will be included herein for purposes of full disclosure. ln the specific instance where the desired result is a substantially uniform distribution of a volume of fluid flow along the length of a slot the first step in the design of a baffle means is the determination of the open area required in the tuned port to be provided. This open area may be the same as the open area of the elongate slot or may be other than that open area, depending upon such factors as the desirability of maintaining uniform velocity through the fluid handling system for the conveying of material, the avoidance of sound such as whistling, or the plenum volumes available within the divided hollow casing.

Once the required open area has been determined, that area is then distributed in a predetermined manner proportional to the distance of an incremental tuned port area from the communicating conduit through which fluid will flow. ln particular, the baffle means functions to mechanically force distribution of the volume of fluid flowing through the hollow casing into a predetermined profile along the length of the slot, by causing fluid flowing within the casing to turn in a direction substantially longitudinally of the slot and then bleed through the tuned port area (see flow lines in FIG. 7). Inasmuch as pressure and velocity distributions of such flow longitudinally of an elongate slot are squared functions reflecting losses encountered, the line defining the edge of the tuned port area of the baffle means should, by mathematic determination, be shaped in accordance with a squared function relation, or be parabolic. However, where the slot through which fluid is flowing becomes of substantial length, such as in an excess of 5 feet, a parabola drawn between zero open area and the required open area most remote from the communication conduit is found to be essentially a straight line. Thus, the distinctions between a parabolic edge for the tuned port and a straight line edge of the tuned port may be ignored for certain applications. Stated differently, as the tuned port opening approaches an infinite aspect ratio, the parabolic curve defining an edge of the tuned port opening becomes an essentially a straight line.

In an instance where the operative connection of a communicating conduit means to a hollow casing is at a location other than the center of length of the elongate slot, the above discussed approach for distribution of tuned port open area still applies. However, the total open area required is distributed on the two sides of the communicating conduit means location in the same proportion as the division of the slot area relative to a line through the communicating conduit means center, where a uniform distribution of a volume of fluid flow along the slot is desired.

Nonuniform distribution of the volume of fluid flowing through the slot is obtained by variance from a squared function relation in determining the distribution of tuned port open area relative to the slot.

Referring particularly to the construction of the hood 3!, it is to be noted that the baffle means includes a horizontally extending plate 39 disposed between the front and rear walls 34, 36 (FIGS. 3-5) and defining with the front wall 36 a pair of open areas 39A and 398. It is to be noted from FIG. 5 that the open areas 39A and 39B are so distributed relative to the position at which the coupling conduit 38 directly communicates with the interior of the hood hollow casing that the baffle plate 39 extends from the rear wall 34 entirely to the front wall 36 in an area immediately beneath the location of operative communication established by the coupling conduit 38. This is done in order to divert fluid flow from the shortest flow path which could be followed in the absence of the baffle means, as mentioned above. Further, the portions of the opened areas 39A and 398 more closely adjacent the location of communication between the conduit 38 and the hollow casing are of lesser width, thereby restricting the volume of flow in those areas. The greater width of the open areas 39A and 398 at locations more remote from the coupling conduit 38 results in greater volumes of air flow passing through those areas. By the distribution of air flow through the nonuniformly distributed open areas 39A and 39B of the baffle means, the desired uniform distribution of the volume of flow along the slot 35 of the hood 31 results.

Similarly, a baffle means including a baffle plate 29 is provided within the air distribution box 21 of the air supply means. In this instance, as shown in FIG. 7, the baffle plate 29 defines with a wall of the box three open areas 29A, 29B and 29C with two closed areas being provided directly beneath the communication of the two coupling conduits 27 and 28 with the box 21. The configurations of the open areas 29A, 29B and 29C are such that the volume of air flowing through the port is distributed uniformly therealong, in similarity to the result obtained with the hood as described above.

It is to be noted that the above discussion illustrates obtaining a desired predetermined profile of a volume of fluid flow through an elongate port in one instance where the plenum volume upstream of the port is minimized and in another instance where the plenum volume downstream of the port is minimized. As to the air supply means 20, the downstream plenum is the volume within the building structure and is relatively large, while the upstream plenum is the distribution box 21, which may be of minimum dimensions by incorporation of this invention. In the air exhaust means 30, the building structure volume provides an upstream plenum and the downstream plenum within the hood 31 is minimized by incorporation of this invention. Thus, the use of baffle means having a nonuniformly distributed open area to divert and restrict flow within a hollow casing is shown to be applicable regardless of the direction of flow therethrough. Further, it is to be noted that regardless of the direction of flow, the profiling of flow results from blocking direct fluid flow along the shortest flow path otherwise possible between the elongate slot and a communicating conduit means while diverting fluid flow longitudinally of the slot in a predetermined distribution.

In the drawings and specification, there have been set forth preferred embodiments of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation.

lclaim:

1. In a fluid distribution system including conduit means for containing a fluid flow and a hollow manifold casing of predetermined cross-sectional area interposed between said conduit means and an enclosure for flow of fluid through said casing between said conduit means and said enclosure, said casing having a wall with an elongate slot therein for fluid flow distribution and said slot having an aspect ratio relatively greater than the aspect ratio of said conduit means at the location of communication thereof with said casing, an improvement comprising baffle means having a cross-sectional area less than that of said casing and mounted within said casing between said slot and said conduit means for distributing the volume of fluid flowing through the slot in a predetermined profile therealong by mechanically blocking fluid flow through the interior of said casing and diverting the fluid flow to follow predetermined flow paths longitudinally within said casing.

2. A fluid distribution system according to claim 1 wherein the direction of fluid flow is from said conduit means into said casing and outwardly through said slot.

3. A fluid distribution system according to claim 1 wherein the direction of fluid flow is inwardly through said slot and through said casing into said conduit means.

4. A fluid distribution system according to claim 1 wherein said baffle means defines with said casing a tuned port having an open area distributed relative to said slot in approximation to a squared function affecting fluid flow longitudinally within said casing, said baffle means and said slot cooperating for distributing the volume of fluid flowing through said slot uniformly therealong.

5. In an air handling system including conduit means for containing an air flow and a hollow manifold casing of predetermined cross-sectional area interposed between said conduit means and an enclosure for flow of air through said casing between said conduit means and said enclosure, said casing having a wall with an elongate slot therein for fluid flow distribution and said slot having an aspect ratio relatively greater than the aspect ratio of said conduit means at the location of communication thereof with said casing, an improvement comprising baffle means having a cross-sectional area less than that of said casing and mounted within said casing between said slot and said conduit means for defining with said casing a tuned port distributed relative to said slot in a predetermined nonuniform manner approximating a predetermined mathematical function and for distributing the volume of air flowing through the slot in a predetermined profile therealong by mechanically blocking air flow through the interior of said casing and diverting the air flow to follow predetermined flow paths longitudinally within said casing while bleeding portions of the air flow through said tuned port to said slot.

6. An air handling system according to claim 5 wherein said conduit means includes a plurality of coupling conduits directly connected to said hollow casing and wherein said baffle means has a cross-sectional area distributed relative to said slot in approximation to said mathematical function. and further in ratio to the position of said plurality of coupling conduits to one another and to said slot.

7. An air handling system according to claim wherein said conduit means includes a single coupling conduit directly connected to said hollow casing and wherein said baffle means has a cross-sectional area so distributed as to define with said casing a pair of generally triangular open areas diverging one from the other longitudinally of said slot.

8. In a flowing gas material conveying system including conduit means for containing a flow of gas and material conveyed by the gas and a hollow manifold casing of predetermined cross-sectional area interposed between said conduit means and an enclosure for gas and material flow through said casing between said conduit means and said enclosure, said casing having a wall with an elongate slot therein for flow distribution and said slot having an aspect ratio relatively greater than the aspect ratio of said conduit means at the location of communication thereof with said casing; an improvement comprising baffle means having a cross-sectional area less than that of said casing and mounted within said casing between said slot and said conduit means for defining with said casing a tuned port distributed relative to said slot in a predetermined nonuniform manner approximating a predetermined mathematical function and for distributing the volume of flow through the slot in a predetermined profile therealong by mechanically blocking flow through the interior of said casing and diverting the flow to follow predetermined flow paths longitudinally within said casing while bleeding portions of the air flow through said tuned port to said slot, the open areas of said slot and said tuned port cooperating for maintaining the velocity of gas flow through said conduit means and casing at least equal to a predetermined velocity for continuing flow of conveyed material. 

1. In a fluid distribution system including conduit means for containing a fluid flow and a hollow manifold casing of predetermined cross-sectional area interposed between said conduit means and an enclosure for flow of fluid through said casing between said conduit means and said enclosure, said casing having a wall with an elongate slot therein for fluid flow distribution and said slot having an aspeCt ratio relatively greater than the aspect ratio of said conduit means at the location of communication thereof with said casing, an improvement comprising baffle means having a cross-sectional area less than that of said casing and mounted within said casing between said slot and said conduit means for distributing the volume of fluid flowing through the slot in a predetermined profile therealong by mechanically blocking fluid flow through the interior of said casing and diverting the fluid flow to follow predetermined flow paths longitudinally within said casing.
 2. A fluid distribution system according to claim 1 wherein the direction of fluid flow is from said conduit means into said casing and outwardly through said slot.
 3. A fluid distribution system according to claim 1 wherein the direction of fluid flow is inwardly through said slot and through said casing into said conduit means.
 4. A fluid distribution system according to claim 1 wherein said baffle means defines with said casing a tuned port having an open area distributed relative to said slot in approximation to a squared function affecting fluid flow longitudinally within said casing, said baffle means and said slot cooperating for distributing the volume of fluid flowing through said slot uniformly therealong.
 5. In an air handling system including conduit means for containing an air flow and a hollow manifold casing of predetermined cross-sectional area interposed between said conduit means and an enclosure for flow of air through said casing between said conduit means and said enclosure, said casing having a wall with an elongate slot therein for fluid flow distribution and said slot having an aspect ratio relatively greater than the aspect ratio of said conduit means at the location of communication thereof with said casing, an improvement comprising baffle means having a cross-sectional area less than that of said casing and mounted within said casing between said slot and said conduit means for defining with said casing a tuned port distributed relative to said slot in a predetermined nonuniform manner approximating a predetermined mathematical function and for distributing the volume of air flowing through the slot in a predetermined profile therealong by mechanically blocking air flow through the interior of said casing and diverting the air flow to follow predetermined flow paths longitudinally within said casing while bleeding portions of the air flow through said tuned port to said slot.
 6. An air handling system according to claim 5 wherein said conduit means includes a plurality of coupling conduits directly connected to said hollow casing and wherein said baffle means has a cross-sectional area distributed relative to said slot in approximation to said mathematical function and further in ratio to the position of said plurality of coupling conduits to one another and to said slot.
 7. An air handling system according to claim 5 wherein said conduit means includes a single coupling conduit directly connected to said hollow casing and wherein said baffle means has a cross-sectional area so distributed as to define with said casing a pair of generally triangular open areas diverging one from the other longitudinally of said slot.
 8. In a flowing gas material conveying system including conduit means for containing a flow of gas and material conveyed by the gas and a hollow manifold casing of predetermined cross-sectional area interposed between said conduit means and an enclosure for gas and material flow through said casing between said conduit means and said enclosure, said casing having a wall with an elongate slot therein for flow distribution and said slot having an aspect ratio relatively greater than the aspect ratio of said conduit means at the location of communication thereof with said casing, an improvement comprising baffle means having a cross-sectional area less than that of said casing and mounted within said casing between said slot and said conduit means For defining with said casing a tuned port distributed relative to said slot in a predetermined nonuniform manner approximating a predetermined mathematical function and for distributing the volume of flow through the slot in a predetermined profile therealong by mechanically blocking flow through the interior of said casing and diverting the flow to follow predetermined flow paths longitudinally within said casing while bleeding portions of the air flow through said tuned port to said slot, the open areas of said slot and said tuned port cooperating for maintaining the velocity of gas flow through said conduit means and casing at least equal to a predetermined velocity for continuing flow of conveyed material. 